Substantial work and advances have recently been made in the field of holographic data storage and retrieval systems. Such systems have very high storage densities, are readily and inexpensively duplicated, do not deteriorate with time and have, therefore, substantial advantages over more conventional systems employing magnetic tapes or discs, punched cards or tapes, etc.
The commonly owned, copending U.S. patent application Ser. No. 254,589, filed May 18, 1972, now U.S. Pat. No. 3,849,766 for "DATA STORAGE AND RETRIEVAL SYSTEM", the disclosure of which is incorporated herein and made a part hereof by reference, describes in detail a prior art holographic data storage and retrieval system particularly adapted for high speed and relatively inexpensive verification systems for making credit checks, identifying persons, permitting access to restricted areas, authenticating airline tickets and the like. The system described in that application enables the determination of whether or not the holder of an identifying or authorizing instrument such as a credit card, identity card, ticket or the like is entitled to what the instrument appears to entitle him. The disclosed system can significantly reduce credit frauds, unauthorized entries to restricted areas and the like.
In general terms, such prior art verification system compares an identifying symbol, mark, description, letter or number, hereinafter sometimes collectively referred to as "number", with a memory of a group of some such numbers. The number group may, for example, represent the bad credit risks or a stolen card within a credit card system. When a check is made the number of the card holder is compared with the number in the memory to determine whether or not the reference number matches a recorded number. The absence of a match indicates that no abnormal condition exists and, for example, that the customary credit or service can be extended to the card holder, or that he may be admitted to a given area. If a match is found, the operator is advised that an abnormal condition exists. The operator may further be advised that credit or access is to be refused or restricted.
The prior art device is intermittently updated by replacing or updating its holographic memory and is placed at each check-point and addressed each time the operator is about to extend credit, permit access or the like. The holograms are recorded in longitudinal rows on a strip of photographic film such as a length of 35mm film. The film strip is moved parallel to the rows past a read station and laser light is directed to a particular row to reconstruct images of the hologram. The images are serially sensed and each sensed image is compared with a given number to be verified.
The memory itself is a film strip with a plurality, e.g. 40 rows, of independent holograms recorded side-by-side. The numbers in the sub-group are randomly assigned to the film rows of channels and each hologram stores one credit card number. Predetermined digits of the number, say the first two or three, are used for randomly assigning the numbers to a channel. When a number is to be verified it is keyed into the system, the appropriate channel is addressed by directing the laser beam therethrough and the film is then advanced past the beam. A spot pattern is generated by each hologram passing the beam. The spot pattern is compared with the keyed-in number to find the presence or absence of a match.
This prior art system represents a very significant advance over systems theretofore proposed. The supporting hardware is relatively inexpensive to construct so that it made it economically feasible to place a unit at each check-point, e.g. at each cash register. Further economies could be obtained by multiplexing a unit to a plurality of check-points. However, the system exhibited some inflexibility because it was generally limited for use with only one type of number, e.g. a given type of credit card. Furthermore, as is more fully described hereinafter, the memory employed in that system duplicates substantial amounts of identical data and is therefore relatively bulky. Also, the manner of recording the numbers on the different film channels frequently yielded grossly disproportionate channel lengths when the numbers within a credit card system, for example, were not random numbers. This in turn leads to a waste of film material and increases average memory access times.